Simple definition
VMware vSAN aggregates local storage resources from multiple ESXi hosts to provide a distributed datastore.
Technical definition
VM data is stored as objects distributed across cluster nodes according to storage policies that define protection and placement requirements.
What is it used for?
Provide shared hyperconverged storage for VMs without requiring a dedicated external SAN array.
Practical example
A multi-host ESXi cluster can place components of a virtual disk on different nodes to tolerate a failure according to the assigned policy.
Common issues
- Insufficient capacity or failure domains to satisfy the storage policy
- An unstable or undersized vSAN network
- Disks, disk groups, or objects are degraded
How it works / role
When a VM writes data, vSAN places the object components according to the storage policy and current cluster state. Hosts coordinate access through the vSAN network and resynchronize or rebuild components when topology or availability changes.
Related terms
Key takeaway: Exact behavior can vary by version, product, and architecture; always validate on the environment actually deployed.